Volume control for amplifiers



T. A. BENNER 2,512,994

2 Sheets-Sheet 1 l I I l I I I I I I I I I g I I I I I I I I i I I I ATTY VOLUME CONTROL FOR AMPLIFIERS June 27, 1950 Filed March 29, 1946 T. A. BENNER VOLUME CONTROL FOR AMPLIFIERS `lune 27, 1950 2 Sheets-Sheet 2 Filed March 29, 1946 Ill' WNN

T AENNER ATTYL Patented June 27, 1950 VOLUME CONTROL FOB AMPLIFIERS v Theodore A. Benner, New York, N. Y., assigner to Airplane & Marine Instruments, Inc., New

York, N. Y., a corporation of New York v Application March 29, 1946, Serial No. 658,033

This invention relates to a control transmission system wherein there is employed a repeater unit 'device for-automatically strengthening when necessary, and maintaining, the line voltage to field stations Where the controls are to be received, the invention having for example to provide a construction which is more efficient in operation and less costly to install and maintain than those heretofore proposed. .l

With these and other objects in vievvvthe invention resides in the novel details ofconstruction and combinations of parts as will be dis,- closed more fully hereinafter and particularly covered by the claims. Y I,

Referring to the accompanying drawings form,- ing a part of this specification and in which like numerals designate like parts in all the views,

zFig. 1 is a representative Wiring diagram of a control system in which this invention is em- .the line voltage, often sufiicient to cause `a nonperformance of some mechanism at a eld station which, particularly in railway signal and control transmission, would be very serious since it might cause accidents and/or loss of life, though it is a fact that in recent years railway control systems havev been designed so that `any failure and/or non-performance would. give a danger signal and hence such failure would be on the side of safety. Hence, by this inventiona repeater unit is inserted in the system in order to boost when necessary and automatically maintain the line voltages for signal operations to'a degree at least sufiicient to permit the u'sual'and intended signal and/or control to be transmitted to the desired eld station and to operate the`v mechanism thereat. i v

More specifically the system as illustrated in Fig. 1 comprises a control oice'at which there is located a plurality of electronic transmitters for sending the controls out over Aline Wiressuch Vas Ll and L2 to the pluralityof field stations at which the controls are to be effective.l Said `transmitters are preferably arranged in groups for Sets, one group associated withelectronic con- 5 5 l, 2 clainl'ls. (Civita-171)l trol 4receivers at one geographic section or loca- .tion in the system, and another group of transmitters associated Wtih other electronic receivers at a different geographic location in the system.

A commutator device is also provided at the control oflice for governing the transmission, at successive intervals, ofthe frequencies generated by the transmitters, said commutator device havingapreferably a member movable over i'lxed contacts by which the successive transmission is accomplished. The transmitters of agroup are adapted to create currents of different frequencies, a frequency for each of the transmitters of the-group, and the transmitters of each of the other groups also have the ability to provide different frequencies, but the transmitters and the frequencies thereof in any one group may be duplicated by and in the transmitters of each of the other groups there being illustrated, merely for simplicity of understanding, -two groups of such transmitters in Fig. 1. Also it should be statedvthat thefeature of station selection is accomplished by using diierent frequency pulsing rates for each geographic group of receivers.

Hence, at the control oice there lis provided a plurality of electronic transmitters identified as 20, 2l and 22 constituting one group, and another groupof electronic transmitters 23, 24 and 25,

.the transmitters of the second group being duplicates respectively of the'transmitters of said first named group. However, the output frequency of transmitter 20 isdiiferent from that of transmitter 2|, land the output frequency of transmitter 22 is different from that of 20 and 2|; and similarly the output frequencies of transmitters 23, 24 and 25 differ from each other but are respectively the same as the'frequencies of transmitters 20,2l and'22. vEach of these transmitters is-substantially'the same as the electronic transmitterparticul'ar-ly illustrated and described in a co-pending application for patent by Harry W.

shaft 26 to Whichis given a substantially constant speed of rotation, and upon said shaft for rotation therewith is mounted an arm 2l the free end of which successively engages a series of contacts identified bythe numerals from I to 8,.,said contacts being cir'cularly arranged in this design, and spaced from each other, and having relatively fixed relation With'respect to the rotating arm. O-ne terminal of transmitter 2i is connected as by th-e wires 28and 2S to contact I with aV branch 30 ,leading to contact 4, one of the terminals of transmitter 22 being in parallel relation with the wire 28. The other terminals of transmitters 2| and 22 are connected in parallel'relation with the wires 3| and 32 to the line Wire L|, and the rotating arm 21 is directly connected to line Wire L2. Transmitter 20 has one of its terminals connected as bythe Wire 33 to wire 32, and the other terminal connected as by thewire 34to wire 29 with a manual test Switch, generally identified by the numeral 35, in the Wire connection 34.

In similar manner transmitter 23has, one terminal connected as by the wires 35 and 31 to the commutator contact numbered 5, with a duplicate manual test switch BBinSertedinthe wire connection 35; and the transmitters 24 and 25' have one terminal of each connected in parallel.

to line Wire Ll as by the wires 39 and 4B, the other terminals of these transmitters being parallelly connected as by-the wir-e 4| to Wire 31'; and lastly the other terminal of-'transmittera23 vis connected as by the wire 42 .to Wire 40.1 There'- fore, itwill be evident from these connections vthat the output of the. transmitters are succes-` 'the yarm, then additional contact'membersare connected to those transmitters whosefrequencies are to have their rate of pulsations increased o wherefore, as an illustration,the Wire' 30 .has been shown connected to contact member 4 -so that the frequency of pulsation of transmitters 20,'2I and 22 is doubled.

In the field there isprovided one group of electronic receivers 50, and 52`which are connected in parallel as by wires 53 and 54 toline Wires LI and L2, and at a different geographic location there is provided another group of similar receivers 55, 56 and 51 connected to said line Wires as by the wires 58 and 59. These-receivers are substantial duplicates of the electronic receiver particularly illustrated and vdescribed, in

` the (zo-pending application of Harry'W. Richards led November 2, 1945 under the Serial No. `626,- 343. The one group comprising receivers 59 5| and 52 are controlled by the group of transmitters 20, 2| and 22 at the control oliice, andthe other group of receivers is controlled by thegother y group of transmitters at said oice.

Fundamentally the similar receivers A5l) and 55 are tuned to be responsive to the high frequency output of transmitters 29 and 23, and the similar receivers 5| and 56 are tuned to be responsive to the high frequency output of transmitters 2 land 2-4, and the similar receivers 52 and 51 are tuned to be responsive to the high frequency 'output of l transmitters 22 and 25. However, the rate of pulsation of the emanated frequencies is adetermining factor in the selection of the transmitted control bythe one or the other group of receivers. That is to Say, for example, if the rate of pulsation is 500 then the receivers 55.,v 55 and 51 only will respond to the transmitted control, but if the rate of pulsation is 1,000 then the receivers 50 5I and 52 only will respond to the transmitted control. Thus it will'be seen that the commutator device constitutes' almeans for selecting the particular group of receivers to be actuated at the desired geographic field locations, as well as constitutes a means for impressing the control frequencies on the line.

At some point in the line, as found necessary, a repeater unit is inserted for the purpose of strengthening the level of the electrical energy utilized by the controls to the exclusion of other energies which may be presenten the line by virtue of the line Wires (according to this invention) being any existing wires and which therefore may be in use for transmitting other utilities That is tovsay, it is to be understood that any existing line wires may be used for this system of control transmission, such as telephone and/ol' pQWer lines, to the end that this control system makes unnecessary the expense of an 'additional pole line facility. It will be further understood thatr the frequencies contemplated according to this invention are those which are well above the audible range.

Referring to Fig. 1, the repeater unit is shown in general diagram as comprising a low-pass filter 10 which is inserted directly in the line, that is to say a ltervwhich is adapted to pass frequencies which are below 175 kc. for example, said filter-being of a standard type and having its arrangement of inductances andv capacities substantially as shown in Fig. 2.

The repeater unit provides pluralfpaths for the transmission of signal and/or control frequencies therethrough; one fpathbeing normal and -used when there hasv been substantially no abnormal line loss, and another path being utilized vin which a weakened receivedA signal is amplified and returned to the line in strengthened condition to be effectively received by receivers therebeyond. By useof the low-pass filter 1D, there can be no feed back of the amplied signal to the input side of the'repeater unit, since said filter serves to block all frequencies above substantially Also, there is provided aj high-pass lter 1| of va standard type, the inductances and capacities of which may be according to the-showing in the diagram of Fig; 3, said lter on one side being connected as'by the Wires 12 and 13 to the line Wires LI and'LZ leading `into the repeater unit, the other side of said "lter being connected'as by the Wires 14 'and 15 tothe input side of an amplifier generallyr designated by the numerall 1B and illustrated in detail in Fig. Ll. The opposite vside of said amplifier is connected as by the wires '11 and 18, to' one Side 0f a duplicate high-Pass filter Nidentified at'19,- the other side'cf said lter being connected as by the Wires y and 8| to the line wires `Ll and L2 Vleading away from the repeater unit.

An electronic receiver 9|)y is provided'con nected on one side as bythe Wires 9| and 92 to wires 14 and 15 respectively, and connected on another side as by the wires 912 'and 94 t0 a .slow-release relay having triple interconnected andpivoted armatures for movement in unison as indicated. The armature 96 is` connected throughl its pivot and Wire 91 to Wire 12, said armature when attracted by said relay'closing withV its front contact which is connected by wire 98 to Wire'80. In similar manner'armature 99 .is connected through its pivot and Wire |00 to Wire 13, andv when attracted by said yrelay closing with its front contact which .is connected by Wire 'to wire'8l'. The third armature |02 serves as a switch in the amplier operating 'battery supply circuit.y The `receiver 9!! istun'ed to be responsive solely to the high frequency of transmitters 20 and 23 at the control office.

By this construction it will be understood that under all conditions all of the impressed frequencies will be received from the line, pass into and through the repeater unit, and back to the line. If the impressed frequencies be received in their normal strength, they will pass unaffected through said repeater, said frequencies taking the path comprising wires -12--13, 91| 00, 98-|0|, .and 80-8I and simultaneously the frequency of transmitters 20 and `23 will pass by wires 12-13 and 9|-92 to receiver 90 thereby causing energization of the magnet of relay 95 to attract its plural armatures and thus maintain continuity of circuit through armatures 96 and 99 and causing the battery circuit of the amplifier to be opened by armature |02. Whereas, under these conditions, all the control frequencies may reach amplifier 16 over wires 14 and 15, yet the amplier will not be affected due to the open condition of the battery circuit operating the same.

As hereinbefore stated the receiver 90 is tuned for response solely to the high frequency of control oice transmitters 20 and 23, but it is believed that further statements should be given with respect to the functioning of saidl receiver. 'Ihis receiver may be a duplicate of that illustrated in Fig. 4 of the aforementioned Harry W. Richards application for Patent Serial No. 626,343 with the exception that, instead of the Richards relay shown associated therewith, there is now contemplated a slow release relay 95. The reason for this is to permit the armatures of said relay to remain closed during the time intervals (respective the commutator device) between the effective impressions of the operating frequencies on the line which are in accordance with the responsiveness of receiver 90. In other words, the release time for the relay 95 is greater than any possible time interval during which the rotating arm 21 in any one revolution may not connect the operating frequency for receiver 90 to the line.

The receiver 90 and its associated relay 95 are so adjusted as to cause operation of the relay at a definite predetermined signal strength as measured at the input terminals of the repeater. In other words, said relay will be energized at and above said predetermined strength to cause straight-through transmission of the frequencies by virtue of Wires |31- |00 and 98-|0|`, but when the signals are below said predetermined strength then said relay will become deenergized and all.

of its armatures will drop to break said straightthrough path and to close (through armature |02) the battery circuit for the amplifier, whereupon the amplifier will function to reestablish the predetermined strength in a manner as willbe disclosed later.

Coming now tc Fig. 4 there is illustrated therein the wiring of the amplifier` generally identified vby the numeral 16. The input side of said amplier comprises the terminals for wires 14 and 15, which terminals are connected to opposite ends of the primary of atransformer, with suitable blocking condensers as shown, the secondary of said transformer having one end thereof connected to chassis ground, and the other end connected as by the wire H2 to the control grid of a suitable input voltage amplifying tube. generally identified by the numeral |13. The plate of said tube is connected by the wire ||4 to the primary ||5 of a coupling :transformen which;

primary isconnected by wire H6 to the back c ontact '||1 in the-battery supply circuit controlled by armature |02 of relay 95 heretofore delscribed,vsaid armature being connected to battery as indicated.

`The-resistor I|`8' connects wire IIE with the Ascreenl 0f said tube inorder to supply operating current from the battery to the tube screen. The suppressor grid of said tube is connected by wire ||9 to chassis ground through a by-pass condenser |20. The cathode of said tube is connected by wire |2| to chassis ground throughan inserted inductance |22 and the biasing resistor |23,A and said'wire |2| is connected by wire |24 to Wire ||9 to hold the cathode and the supressor grid at the same potential as well as to furnish a high frequency by-pass to chassis ground.

The secondary |30 associated with primary I5 is connected at its ends to the terminals on one side of a corrective network, the terminals on the opposite side thereof being` connected as by the wires |3| and |32 to the terminals on one sideof an attenuation network, the opposite terminals of which are connected to ends of the primary |33 of a, transformer whose secondary-|34 has one end thereof connected to the grid of the output tube |35 as by the Wire |43. The corrective network may be of standard design las indicated, having components which may be varied in order to compensate for diiferences in line attenuation for various frequencies employed in the control system, thereby correcting inequalities in the strength of the signal received by Athis amplifying unit. v

The attenuation network may also be of standard construction but provided with means for manual adjustment whereby the variable resistors such as |36, |31 and |38 will be actuated in unison by a single dial to regulate the desired level of output at terminals 11 and 13 for condi.- tions considered normal.

The plate of the output tube |35 is connected by the wire |39 to one end of the primary |40 of the output transformer, the other end of said primary being connected as by the wire I4! to the back Contact ||1 heretofore described. Said primary |40 has a tap leading to the screen of said tube and having a resistor |42 therein. The cathode of said tube is connected as by the wire |44 to chassis ground through the resistor |45 and also through e, by-pass condenser |46. The grid of said tube is also connected to chassis ground as by the Wires|41 and |48, the former having the resistor |49 therein, and the other end of the secondary' |34 is connected as by the wire |50 to wire |41.

The primary |40 of the output transformer has a secondary the ends of which are connected through suitable terminals to wires 11 and 18 heretofore described, the circuit being controlled through the front contacts of a, relay |11. Said primary also has another secondary such as |56 having a variable condenser |51inserted at its center tap, one end of said secondary |56 going to chassis ground and the other end connectedby wire |58 to a uni-directional current Aflow device such as selenium rectifier indicated at |59, from which wire |60 leads to a junction i3! between the inductor |22 and resistor |23. A branch of wire |60 is connected as by the wire |1| to the grid of a control tube |12.

Thus it will be seen that the output transformer comprising primary |40 and its secondary |55 constitutes the` meansl for feeding the amplified signal to the line wires, andthat the primaryl and its other secondary |56, together with the variable condenser |51 and rectiiier |59,in combi nation with resistor |23, inductor |22 and condenser I20, constitutes an automatic gain regulation circuit for maintaining a predetermined range of` levels for the output signal, as measured across the wires 'l1-18,3in accordance with.A the adjustment initially set upbetween the corrective and attenuation networks to satisfy operating conditions.

The predetermined range of output levels thus established includes the desired level for which the attenuation network was adjusted, and further said predetermined range is solely in .ac-`

cordance with a particular and safe-operating range of energy levels received at the input. stage of this amplifier unit or repeater. That is to'say, it is intended to have this amplifier operate effectively only on variations of input energy which are to be expected because of changes in weather conditions, wherefore when abnormal and/or fault conditions affect the input energy beyond a safety factor, the amplifier will be ineective, due to the incorporation therein of any suitable mechanism such as a relay |11 which will open the amplifying circuit, but which will close the circuit after the fault condition has passed. The relay |11 is energized by current supplied to one side of its coil as by the wire |13 connected with wire i4! at the junction point |14, the other sidev of the relay coil being connected as by the .wire

|15 to the plate of the control tube |12.y Tube |12 is biased through the variable resistory |15 which is so adjusted that the relay will become deenergized when the signal outputV across the wires 11 and 18 falls below a predetermined level, due to said abnormal and/or fault conditions.

Further, the circuit comprising primary |40 combination with the condenser |20, is to cause` a smoother action in the above mentioned regulation when a pulsing signal such as described heretofore is received by the amplifier.

It will be understood thatall of the structural features of the amplifier must be coordinated and, using the resonant frequency to which. the automatic gain control circuit is tuned as a reference point, the design and regulation ofthe corl rective and attenuation networks must 'bebuilt around and adjusted thereto in accordance with the local operating conditions. Further, the intent of the invention is to provide a device that will operate without an attendant, on the side of safety, and with a minimum of maintenance including adjustments, since the initial adjustment is made to meet the maximum expectedyariations of line loss.

When the conditions, which' cause abnormal;

loss, areV remedied and the received signal atr the to become energized and attract its armatures,`

whereby armatures 96 and 99 will connect:.the

wires 91-|u with the wires: iaslui to reestablish the straight-through path for the received signal, and simultaneously through armature 02 W-ill open the battery circuit to render amplier 16 inoperative.

The foregoing description has been with krespect to transmission of signals and/or controls in one direction only in the system, namely, from left to right as seen in Fig. 1. It may however be desirable in some systems to provide for a, transmission of signals, indications, and/or controls from the field back to the control office, or in a, direction reversel to that previously considered. In such a case there will be electronic transmitters ateld locations, `which transmitterswill be connected in multiple with the field receivers now shown in Fig. 1,-and there will be electronic receivers at the control office, which receivers will be connected in multiple'with the control oiiice transmitters now shownv in said figure, the operation of which newly considered transmitters and receivers will be the same except that their control energy will have reverse flow. However, it will be realized that frequencies employed for such reverse transmission must be in a band which is different from the band utilized for the opposite transmission.

Therefore, in Fig. l there has been indicated a` third transmission path in a repeater unit,

, which is a substantial duplicate of the path comprising lters 1| and 1Q and amplifier 15, said duplications indicated by the numerals 1|', 19 and 15',` the amplifier 15'Y carrying the arrow symbol |163 to indicate the directional now in reverse of frequencies in this path, which arrow symbol is reversed with respect to that shown in the path associated with amplier 15. Possibly it would be desirable to provide, in this third and reverse path, band-pass filters of conventional design in place of iilters 1| and 19, and itwould be optional to use a receiverV and associated relay such as 99 and 95 in conjunction with this third and reverse path.

In the appended claimszthe term signals is to be understood as denitive of any utility that may be transmitted by the use of different frequencies impressed upon -line wires, and hence this invention is to cover controls, indications, or any other audibly and/or mechanically oper ated utilities or devices, and not to be limited specifically to signals alone. Further, this invention isv applicable to the amplification of any transmitted current frequency for any purpose, and hence is not to be limited to the application thereof to railway systems alone.

It is obvious that those skilled in the art may vary the details of construction and arrangements of' parts without departing Yfrom the spirit of. this invention, wherefore it is desired not to be limited to the exact foregoing disclosure except as may be required by the claims.

What is claimed is:

1. An electronic amplifying unit for a system of .signal transmission wherein different signal operating frequencies are impressed on and carried over line wires, and wherein a desired predetermined range of energy output for a signal is established, said unit comprising an input stage and an output stage, and a circuit including an automatic switching device as well as an. electronic control therefor,v said circuit for automatically regulating the output energy to within the established predetermined range, onel portioncf said circuit comprising a rectifier and a Yresistor connected serially to ground at one-end ,9 thereof, said circuit portion having an interposed transformer secondary at the output stage tuned to be responsive to one of the signal operating frequencies and connected to ground at the other end of said portion, and another portion of said circuit connected in multiple with the resistor of said first named portion and comprising an inductor and a condenser connected serially to ground, said second named portion having a connection with the input stage intermediate said inductor and said condenser.

2. An electronic amplifying unit for a system of signal transmission wherein different signal operating frequencies are impressed on and carried over line wires, comprising an input stage and an output stage between which is disposed a network for correcting inequalities in the received signal strength, an attenuation network manually adjustable initially to establish the desired predetermined level of energy output for the signal, and a circuit including an automatic switching device as well as an electronic control therefor, said circuit for automatically regulating the output energy to within a predetermined ranges of levels, which range includes the desired level for which the attenuation network was adjusted, one portion of said circuit comprising a rectifier and a resistor connected serially to REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,880,889 Doba, Jr Oct, 4, 1932 2,031,539 McCaa Feb. 18, 1936 2,084,135 Ford June 15, 1937 2,137,020 Luck Nov. 15, 1938 2,154,062 Chesnut Apr. 11, 1939 2,325,829 Boswau Aug. 3, 1943 2,379,631 Finckh July 3, 1945 

